Field
Embodiments relate to an apparatus for finishing the edges of articles, especially articles formed of brittle materials. More specifically, embodiments relate to an apparatus for finishing an edge of an article using magnetorheological polishing fluid (MPF).
Technical Background
Glass sheets have been cut by mechanical or laser separation. Mechanical separation leaves the cut glass sheet with a rough and/or sharp edge that makes the cut glass sheet vulnerable to cracking, and likely undesirable for certain applications. In practice, the roughness or sharpness has to be removed, typically by a series of mechanical grinding and polishing steps. Abrasive rotational grinding tools are used to mechanically remove roughness and/or sharpness from edges. Typically, the abrasive rotational grinding tools are metal grinding wheels containing micron-sized abrasive particles, e.g., micron-sized diamond particles. Mechanical polishing can be by a metal, vitrified or polymer wheel, and may or may not employ loose abrasive particles. The mechanism of material removal using the abrasive grinding tools is typically considered to involve fracture. As such, the larger the size of abrasive particles in the grinding tool, the larger the fracture sites that remain on the edge of the glass sheet after grinding. These fracture sites effectively become stress concentration and fracture initiation sites, which result in a finished glass sheet having a lower strength than the parent glass sheet. Grinding tools with smaller abrasives and/or polishing tools can be used to reduce the size of the fracture sites. It is possible to avoid roughness in the edge by using laser separation to cut the glass sheet. However, the laser-separated glass sheet would still have a sharp edge. Typically, a series of steps involving coarse and fine abrasive tools is used to remove the sharpness from the edge. In practice, several polishing steps are typically needed to remove the sharpness, which can significantly increase the cost of finishing the glass sheet. U.S. Pat. No. 6,325,704 (Brown et al.) discloses a system in which a plurality of grinding wheels and polishing wheels are used to simultaneously grind and polish the edge of a glass sheet.